This invention relates to electronic circuits for use on internal combustion automobile engines, and more particularly an open loop electronics circuit for carburetor altitude compensation.
It is well known that changes in air density due, for example, to atmospheric pressure changes effect the operation of a carburetor installed on an automobile engine. Typically, such a change occurs when the vehicle is driven at an altitude other than that for which the carburetor is calibrated. Various schemes of altitude compensation have been tried from time to time to compensate for the effects of atmospheric pressure changes. Society of Automotive Engineers (SAE) paper 760286 describes the problem presented by atmospheric pressure changes and discusses a number of ways of coping with it. The proposed ways include both mechanical and electronic schemes. U.S. Pat. No. 3,899,551 issued Aug. 12, 1975, is an example of the former approach, while U.S. Pat. No. 4,237,833 issued Dec. 9, 1980, is an example of the latter. As shown in the 4,237,833 patent, it is a feature of the various electronic schemes that they include feedback circuitry employing microprocessors or similar devices in which numerous additional sensing features are included. While systems of this type may effectively compensate for atmospheric pressure changes, such systems are both complex and expensive. What is needed, is a simple circuit not requiring feedback or a multitude of associated sensors which is easily installed on a vehicle and readily interfaces with the carburetor to provide altitude compensation.